The present invention relates generally to a suspension trailing arm. More particularly, the present invention relates to a suspension trailing arm having a portion with a generally X-section profile and a suspension assembly incorporating the trailing arm.
Heavy commercial vehicles typically employ trailing arm suspension systems, particularly in relation to axles of trailers of articulated vehicles or, potentially, rear axles of rigid body vehicles.
Heavy commercial vehicles (including trucks, buses and coaches) can be distinguished from light commercial vehicles (such as vans) and light passenger vehicles due to one or more of the following characteristics: 1) a laden weight in excess of approximately 3.5 tonnes and 2) the use of air actuated brakes as opposed to hydraulically actuated brakes (because air actuated brakes are better able to withstand the increased heat generated by the repeated braking of a vehicle having a weight in excess of approximately 3.5 tonnes).
Such vehicles (including associated trailers) also typically employ a pair of spaced parallel beams that run the length of the vehicle and act as a chassis upon which a vehicle body is mounted. The trailing arm suspension system includes trailing arms.
When used in heavy commercial vehicles, a front of each trailing arm is typically pivotally mounted to a chassis beam of the vehicle. Each trailing arm extends rearwardly (i.e., towards the rear of the vehicle) to a mounting position for an axle and then further rearwardly to a mounting surface for an air spring that is mounted between the trailing arm and the chassis beam. Axles in such vehicles are typically substantially rigid beam-type axles (i.e., axles that extend between spindles upon which wheels at opposite sides of the vehicle are mounted). In some circumstances, the orientation of the trailing arms may be reversed to pivot at a rear of the trailing arm, in which case they are known as “leading arms.” For the purposes of this specification, the term trailing arm should also be understood to encompass a leading arm.
Known heavy vehicle trailing arms are typically constructed either from solid spring steel provided with U-bolts and plates to connect the axle to the trailing arm, a fabricated steel plate which is then welded to the axle or an axle adapter, or a hybrid of the two types. An example of a fabricated trailing arm is disclosed in U.S. Pat. No. 5,639,110 (Pierce et al.). Both prior art types of trailing arms provide a rigid connection between the trailing arm and the axle to resist bending, but provide a resilient connection between the chassis and the axle either by flexing the spring steel trailing arm or by flexing a large elastomeric bush (resilient bearing) in an end of the fabricated trailing arm. This enables articulation forces induced during vehicle use to be taken up, while maintaining tracking and roll stability.
It is known from the present applicant's earlier published application WO 2004/054825 to cast or forge trailing arms having an I- or C-section profile and a direct beam-to-axle connection. Such trailing arms provide advantages over fabricated and spring steel arms in terms of their manufacture, strength and packaging.
Cast and forged trailing arms tend to be made with “traditional” beam-type profiles, whereas the applicant has now recognized that there is scope for further improvements to be achieved in strength, durability and weight reduction for trailing arms by moving away from such traditional shapes.